The present invention relates to a packaged column arrangement for an air separation plant of the type having higher and lower pressure columns. More particularly, the present invention relates to such a packaged column arrangement in which an intermediate reboiler is provided in the lower pressure column to condense tower overhead of the higher pressure column, thereby to provide reflux for the both the higher and lower pressure columns. Even more particularly, the present invention relates to such a packaged column arrangement in which the higher and lower pressure columns are positioned within a cold box so that the higher and lower pressure columns are in a sufficiently staggered relationship that the reflux stream flows under the influence of gravity into the higher pressure column.
There are a variety of plant designs and cycles by which air is separated into oxygen and nitrogen. In a common type of air separation plant, air is partially or fully condensed within a bottom reboiler of a lower pressure column. The partially or fully condensed air is then rectified in the bottom of a higher pressure column. The rectification of the air produces a nitrogen rich tower overhead and an oxygen rich column bottoms. Reflux for both the higher and lower pressure columns is produced by condensing a stream of the nitrogen rich tower overhead in an intermediate reboiler positioned within the lower pressure column.
An example of such a plant may be found in U.S. Pat. No. 5,463,871 in which the higher pressure column is placed below a section of the lower pressure column containing the intermediate reboiler. The other section of the lower pressure column, containing the lower reboiler, serves to condense or partially condense the air. Since the intermediate reboiler is located directly above the higher pressure column, reflux flows under gravitational influenced into the higher pressure column.
The distillation column arrangement of U.S. Pat. No. 5,463,871 is mounted within an insulated cold box structure. The cold box for such a plant must have a sufficient height to accommodate the higher pressure column and the lower pressure column section located above the higher pressure column. As is well known in the art, the higher the cold box, the more expense the plant because more materials are used in its fabrication. In addition, the mounting of a three column arrangement is normally effectuated by separate mountings which add to the complexity of the cold box.
As will be discussed, the present invention provides a distillation column arrangement having an intermediate reboiler in which the height of the cold box is inherently less than the prior art and also, the column mounting is less complicated.